Global warming. Observed temperature changes The Earth's average surface temperature rose by 0.74±0.18 °C over the period 1906–2005. The rate of warming.

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Presentation on theme: "Global warming. Observed temperature changes The Earth's average surface temperature rose by 0.74±0.18 °C over the period 1906–2005. The rate of warming."— Presentation transcript:

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Observed temperature changes The Earth's average surface temperature rose by 0.74±0.18 °C over the period 1906–2005. The rate of warming over the last half of that period was almost double that for the period as a whole (0.13±0.03 °C per decade, versus 0.07±0.02 °C per decade). The urban heat island effect is very small, estimated to account for less than 0.002 °C of warming per decade since 1900.Temperatures in the lower troposphere have increased between 0.13 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Climate proxies show the temperature to have been relatively stable over the one or two thousand years before 1850, with regionally varying fluctuations such as the Medieval Warm Period and the Little Ice Age.Earth's average surface temperatureurban heat islandtroposphere°Fsatellite temperature measurementsClimate proxiesone or two thousand yearsMedieval Warm PeriodLittle Ice Age The warming that is evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups. Examples include sea level rise (water expands as it warms), [31] widespread melting of snow and ice, increased heat content of the oceans, increased humidity, and the earlier timing of spring events,e.g., the flowering of plants.The probability that these changes could have occurred by chance is virtually zero.sea level risewaterexpands [31]snow iceheat content of the oceanshumidity timingspringfloweringplantsprobability

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Observed temperature changes The Earth's average surface temperature rose by 0.74±0.18 °C over the period 1906–2005. The rate of warming over the last half of that period was almost double that for the period as a whole (0.13±0.03 °C per decade, versus 0.07±0.02 °C per decade). The urban heat island effect is very small, estimated to account for less than 0.002 °C of warming per decade since 1900. Temperatures in the lower troposphere have increased between 0.13 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Climate proxies show the temperature to have been relatively stable over theone or two thousand years before 1850, with regionally varying fluctuations such as theMedieval Warm Period and the Little Ice Age.Earth's average surface temperatureurban heat islandtroposphere°Fsatellite temperature measurementsClimate proxiesone or two thousand yearsMedieval Warm PeriodLittle Ice Age

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Initial causes of temperature changes The climate system can respond to changes in external forcings.External forcings can "push" the climate in the direction of warming or cooling. Examples of external forcings include changes in atmospheric composition (e.g., increased concentrations of greenhouse gases), solar luminosity, volcanic eruptions, and variations in Earth's orbit around the Sun. Orbital cycles vary slowly over tens of thousands of years and at present are in an overall cooling trend which would be expected to lead towards an ice age, but the 20th century instrumental temperature record shows a sudden rise in global temperatures.greenhouse gasessolar luminosityvolcanicvariations in Earth's orbitOrbital cyclesice ageinstrumental temperature record

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Greenhouse gases The greenhouse effect is the process by which absorption and emissi on of infrared radiation by gases in the atmosphere warm a planet's lower atmosphere and surface. It was proposed by Joseph Fourier in 1824, discovered in 1860 by John Tyndall, was first investigated quantitatively by Svante Arrhenius in 1896, and was developed in the 1930s through 1960s by Guy Stewart Callendar.absorptionemissi oninfraredatmosphereplanetJoseph FourierJohn TyndallSvante ArrheniusGuy Stewart Callendar

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Particulates and soot Global dimmingGlobal dimming, a gradual reduction in the amount of global direct irradiance at the Earth's surface, was observed from 1961 until at least 1990. The main cause of this dimming is particulates produced by volcanoes and human made pollutants, which exerts a cooling effect by increasing the reflection of incoming sunlight. The effects of the products of fossil fuel combustion – CO 2 and aerosols – have largely offset one another in recent decades, so that net warming has been due to the increase in non-CO 2 greenhouse gases such as methane. ] Radiative forcing due to particulates is temporally limited due to wet deposition which causes them to have an atmospheric lifetime of one week. Carbon dioxide has a lifetime of a century or more, and as such, changes in particulate concentrations will only delay climate changes due to carbon dioxide.irradiancepollutantswet depositionatmospheric lifetime

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Solar activity Since 1978, output from the Sun has been precisely measured by satellites. These measurements indicate that the Sun's output has not increased since 1978, so the warming during the past 30 years cannot be attributed to an increase in solar energy reaching the Earth. In the three decades since 1978, the combination of solar and volcanic activity probably had a slight cooling influence on the climate. Climate models have been used to examine the role of the sun in recent climate change. Models are unable to reproduce the rapid warming observed in recent decades when they only take into account variations in solar output and volcanic activity. Models are, however, able to simulate the observed 20th century changes in temperature when they include all of the most important external forcings, including human influences and natural forcings.output from the Sunsatellitesvolcanic activity

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Feedback The climate system includes a range of feedbacks which alter the response of the system to changes in external forcings. Positive feedbacks increase the response of the climate system to an initial forcing, while negative feedbacks reduce the response of the climate system to an initial forcing. There are a range of feedbacks in the climate system, including water vapor, changes in ice- albedo (snow and ice cover affect how much the Earth's surface absorbs or reflects incoming sunlight), clouds, and changes in the Earth's carbon cycle (e.g., the release of carbon from soil). [110] The main negative feedback is the energy which the Earth's surface radiates into space as infrared radiation. According to the Stefan- Boltzmann law, if temperature doubles, radiated energy increases by a factor of 16 (2 to the 4th power).water vaporice- albedosnowicecloudscarbon cycle soil [110]radiatesinfrared radiationStefan- Boltzmann law

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Climate models A climate model is a computerized representation of the five components of the climate system: Atmosphere, hydrosphere, cryosp here, land surface, and biosphere. [119] Such models are based on scientific disciplines such as fluid dynamics, thermodynamics as well as physical processes such as radiative transfer. The models take into account various components, such as local air movement, temperature, clouds, and other atmospheric properties; ocean temperature, salt content, and circulation; ice cover on land and sea; the transfer of heat and moisture from soil and vegetation to the atmosphere; chemical and biological processes; solar variability and others.climate modelcomputerized representationAtmospherehydrospherecryosp herebiosphere [119]fluid dynamicsthermodynamicsradiative transfersalt contentcirculation Although researchers attempt to include as many processes as possible, simplifications of the actual climate system are inevitable because of the constraints of available computer power and limitations in knowledge of the climate system.

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Observed and expected environmental effects "Detection" is the process of demonstrating that climate has changed in some definedstatistical sense, without providing a reason for that change. Detection does not imply attribution of the detected change to a particular cause. "Attribution" of causes of climate change is the process of establishing the most likely causes for the detected change with some defined level of confidence. [134] Detection and attribution may also be applied to observed changes in physical, ecological and social systems. [135]statistical [134] [135]

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Natural systems Global warming has been detected in a number of natural systems. Some of these changes are described in the section on observed temperature changes, e.g., sea level rise and widespread decreases in snow and ice extent. [136] Anthropoge nic forcing has likely contributed to some of the observed changes, including sea level rise, changes in climate extremes (such as the number of warm and cold days), declines in Arctic sea ice extent, and to glacier retreat. [137]observed temperature changessea level risesnowice [136]extremesArctic sea iceglacier retreat [137]